ECM degrading proteases and tissue remodelling in the mammary gland

Matrix degradation and tissue remodelling directed by matrix-degrading proteases are activated in physiological situations such as wound healing and involution of the prostate, ovaries and uterus. Recently, other activities, in addition to the cleavage of matrix proteins, have been attributed to matrix proteases including the release of growth factors from the extracellular matrix and roles in the maturation of adipocytes. This review describes extracellular proteases, including MMPs, plasminogen and cathepsins involved in the tissue remodelling processes that occur in the breast during pubertal mammary development and the mammary cycle of pregnancy, lactation and weaning. It particularly focuses on development and weaning, termed mammary gland involution, when the majority of remodelling occurs. It also brings together recent findings on the exciting new functions of matrix-degrading proteases.